In most known industrial processes in which metallic or conducting films are applied to glass or other non-conducting substrates, such as in commercial mirror production, the adhesion properties of the film (although an advantage) are not of major importance. Subsequent metallic or organic coatings protect the film from damage likely to result in loss of film adhesion.
In other coating processes such as occur in the production of printed circuit boards, a metallic coating is deposited onto a plastic, ceramic or other non-conducting substrate, which has been prepared in such a way as to provide mechanical anchorage for the coating. The surface preparation may require the use of etching, sandblasting or the like. The use of gaseous and chemical reducing agents may also be employed to assist metal deposition on said substrates.
Vacuum vapour evaporation and sputtering are other known methods of producing such coatings on substrates. In these processes, the interface between the substrate and coating is generally distinct, which in many cases produces poor relative adhesion. These processes also produce coatings of limited thickness.
In other known processes such as those used to produce semi-conducting components for the electronics industry, migration of semi-conducting and/or conducting films into the surface of a chosen substrate has been successfully achieved. The films produced by surface migration processes generally exhibit good relative bond strength. However, this is often of little advantage as the subsequent function of these films is not necessarily dependent on the mechanical strength of their surface adhesion.
The main disadvantage of such films arises when it is necessary to increase the thickness or modify the surface migration films. Increase in film thickness is usually achieved by using one of a number of standard techniques, which may include vacuum deposition, electroless plating, ion displacement, and electroplating. The techniques and processes which are currently used to increase film thicknesses are costly, cumbersome, and size restrictive.
Further, it is generally understood that when migration processes produce a surface coating, the coating may exhibit physical and chemical properties which differ from the individual characteristics of the materials involved. It is therefore likely that a conducting or semi-conducting coating, produced by a surface migration process, may exhibit properties which make it difficult or impossible to subsequently increase its thickness.
Some existing processes require the use of an intermediate coating such as an adhesive to produce effective substrate-to-conducting film bond strengths. These composite coatings have many disadvantages, including temperature and solvent sensitivity. In addition, the presence of the intermediate coating may interfere with the subsequent use of the coated substrate.
Additional problems are encountered with existing methods when producing precision delineated patterns of conducting and/or semi-conducting coatings on nonconducting substrates. Stencils, masks, resists, post-etching and the like, are devices and processes currently used to create such delineated patterns of conducting or non-conducting coatings on substrates. Stencils and similar devices are difficult to maintain during the aggressive heating and other physical and chemical treatments used to establish the coating delineation.
Finally, known methods of applying coatings to substrates are generally designed for flat substrates, and are not particularly suitable for curved substrate surfaces.
It is an object of the present invention to provide an improved method of applying a coating to a non-conducting substrate, which overcomes or ameliorates at least some of the abovedescribed disadvantages of prior art coating methods.
It is a preferred object of the present invention to provide a coating technique whereby precision delineation of a conductive or semi-conductive coating pattern can be prepared with accuracy and wherein the precision pattern is maintained during heat treatment or other physical and chemical processing.
It is a further preferred object of the invention to provide an effective means of producing precision delineated conducting or semi-conducting multi-layer coatings on non-conducting substrates.